a(n) is the least prime power (A246655) P such that P-n is the next smaller prime power below P.

Terms

a(0) =3a(1) =7a(2) =16a(3) =23a(4) =37a(5) =59a(6) =1031a(7) =97a(8) =521a(9) =149a(10) =536870923a(11) =211a(13) =307a(14) =65536a(15) =1847a(16) =8209a(17) =1087a(19) =907a(20) =524309a(21) =1151a(22) =549755813911a(23) =4201a(24) =17179869209a(25) =2503a(26) =16411a(27) =2999a(28) =131101a(29) =1361a(30) =34359738368a(31) =5623